they released a new one (if you mean a tourist visa) in january 2008, i believe. my mom printed one out in december and when we checked the website again in january (a week before her interview), we found out that it changed. so we had to use the new one.
what do you mean you bought a visa form? you can just print one out from the website... for free.
edit: hahahah! honey, the one that "costs" $131 is not bought. you print out that bank form from the website FOR FREE then go to the bank to pay for the interview. the form is FREE. the money you pay is for the visa processing. you are not paying for the form.
and by the way, i DO know the answer. i've helped my family apply for their US tourist visas lots of times and i've done so myself as well before i moved to the US.
your visa fees will be valid as long as they do not change the visa processing fees. say, you paid $100 for the visa interview but now they're asking for $131... then you have to pay for the $131. your old one will not be accepted.
and as long as they don't change their application forms, you can use the one you have. if however, it changes from the time you print out yours and the time of the interview (like my mom's case), then you need to use the new one unless it indicates on the website that the old one can be used.